1. Field of the Invention
The present invention relates to a method of aligning a movable mold and a mating fixed mold on a compression molding machine for molding a resin workpiece formed of a thermicset plastic resin or the like, and a device for carrying out the method.
2. Description of the Prior Art
Japanese Patent Laid-open (Kokai) Nos. 60-15119 and 60-30323 disclose compression molding machines for forming automotive front panels, automotive body panels and the like by compression-molding a sheet molding compound (SMC), namely, a thermioset plastic resin sheet.
The compression molding machine disclosed in Japanese Patent Laid-open No. 60-15119 comprises a bed, uprights set upright on the bed, a crown block supported by the uprights, a hydraulic cylinder actuator mounted on the crown block, a slide block joined to the lower end of the piston rod of the hydraulic cylinder and guided for vertical movement by the uprights, and at least a pair of mold position adjusting cylinder actuators fixedly mounted on the bed. An upper mold is fixed to the lower surface of the slide block, and a lower mold is fixed to the bed to compression-mold a resin workpiece in a cavity formed by the upper and lower molds.
In compression-molding a thermioset plastic resin sheet, such as a SMC, on such a compression molding machine, the upper mold must be held in parallel to the lower mold with a high degree of accuracy, on the order of 5/100 mm, to obtain a molding of satisfactory quality. To meet such a requirement, the position of the slide block is adjusted by the mold position adjusting cylinder actuators to maintain the upper mold in parallel with the lower mold.
In adjusting the respective zero points of the piston rods of the mold position adjusting cylinder actuators, the upper mold is brought into close contact with the lower mold, the respective piston rods of the mold position adjusting cylinder actuators are projected by the same length, and then shims are placed between the respective upper ends of the piston rods and the lower surface of the slide block so that the slide block is born evenly on the piston rods.
This zero-point adjusting procedure must be executed every time the mold is changed thus requiring troublesome adjusting work, because different molds are different from each other in height, which requires a stock of many reserve shims and reduces production efficiency. Furthermore, the gaps between the piston rods and the slide block must be measured to select appropriate shims, which entails errors in measuring the thickness of shims and the size of the gaps, and hence it is impossible to achieve the zero-point adjustment with a high degree of accuracy.